1. Field of the Invention
The present invention relates to an X-ray Generator for generating pulse X-rays upon optical pumping.
2. Related Background Art
X-rays of high frequency pulses have conventionally been utilized in the field of diagnosing systems, analyzing systems, and the like. While thermoelectron sources are employed as an electron source of an X-ray generating tube for generating the pulse X-rays, the pulse repeating period of X-rays generated thereby is on the order of nanosecond or greater due to restrictions in terms of electronic circuit.
When an optical pumping electron source is employed as the X-ray generating tube, by contrast, the pulse repeating period of generated X-rays can be shortened to the order of picoseconds by pumping with high-frequency pulse light. Such an optical pumping X-ray generating tube is disclosed in Japanese Patent Application Laid-Open No. SHO 52-142984 and No. HEI 4-12497, for example.
For generating high energy X-rays in an optical pumping X-ray generating tube, it is necessary that an X-ray target be bombarded with photoelectrons at a high speed released from a photocathode. Applying a high voltage between the photoelectron releasing layer and the X-ray target in order to accelerate photoelectrons, however, may be problematic, for example, in that discharge may occur between these electrodes, whereby pulse X-rays may not be generated favorably.
In order to overcome the problems mentioned above, it is an object of the present invention to provide an X-ray Generator which can generate pulse X-rays having a high energy and a high frequency.
This X-ray Generator comprises a light source for emitting pulsed laser light; an X-ray generating tube having a photoelectron releasing layer for releasing a photoelectron in response to the laser light incident thereon, an X-ray target for emitting an X-ray when bombarded with the photoelectron accelerated, and an exit window for emitting the X-ray to the outside; and a voltage control section for controlling a pulsed acceleration voltage applied between the photoelectron releasing layer and the X-ray target in order to accelerate the photoelectron; wherein the acceleration voltage is at a pulse top voltage at least until the X-ray target is bombarded with the photoelectron after the photoelectron is released from the photoelectron releasing layer.
In this configuration, control is effected such that the pulse top voltage (highest voltage of pulse voltage) is applied between both electrodes of the photoelectron releasing layer (cathode) and the X-ray target (anode) at least during the time from the release of a photoelectron to the bombardment therewith, whereby the rising and falling of an acceleration voltage can be set so as to yield such a narrow pulse width that no discharge occurs between the both electrodes. This can raise the pulse top voltage, thereby enabling the photoelectron to attain a higher speed (outputted X-rays to attain higher energy).
The X-ray Generator may further comprise a beam expander for enhancing a spot diameter of the laser light incident on the photoelectron releasing layer. This allows the photoelectron releasing layer to emit a sufficient amount of photoelectrons and can reduce damages to the photoelectron releasing layer.
The X-ray Generator may further comprise dividing means for dividing the laser light from the light source into incident light to be made incident on the photoelectron releasing layer, and control light for controlling the acceleration voltage by way of the voltage control section. This makes it possible to easily acquire a control optical pulse in synchronization with an optical pulse for releasing photoelectrons.
The X-ray Generator may further comprise delay means for delaying the incident light by a predetermined time. This can retard the photoelectron releasing timing by a predetermined time with respect to the rising timing of acceleration voltage.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.